Up to now, flavorings or taste improvers and the like obtained by carrying out a protease treatment of milk and dairy products have been proposed. So far, it has been proposed a method for producing a natural flavoring for dairy products comprising an enzyme treated product obtained by allowing a protease treated product of whey to contact with an adsorbent and then eluting with an ethyl alcohol solution (Patent Reference 1). However, the method described in Patent Reference 1 requires a large scale device for adsorption by the adsorbent and elution, and its operation was complex. In addition, there was a problem of losing a raw milk feeling and a thickness caused by the adsorbent.
Flavorings or taste improvers obtained by carrying out a protease treatment and a lactic acid fermentation of milk and dairy products have also been proposed. For example, an aromatic substance prepared by heating a liquid product obtained by subjecting a dairy product containing carbohydrates to an enzymatic protein hydrolysis and (or) lactic acid fermentation (Patent Reference 2). In addition, there has been reported a seasoning in which a lactic acid bacterium is inoculated into cheese whey which is then divided into a precipitation portion containing protein as a main component and a supernatant portion by carrying out centrifugation under heating or without heating, and the precipitation portion is treated with a protease and mixed with the supernatant portion (Patent Reference 3). However, since the flavor enhancers obtained by the methods described in Patent References 2 and 3 contain a large amount of sugar in the dairy products which become the substrate, when heated after the protease treatment, Maillard reaction which is a reaction of amino acids with reducing sugars is generated so that a scorched odor, a caramel odor or a nuts-like odor is generated, thus resulting in a rich flavor enhancer having a flavor of baked food but not having a flavor of fresh raw milk.
In addition to these, it has been proposed to allow a lipase, a protease and a lactic acid bacterium to act upon a substrate containing a milk fat such as fresh cream (cream), or butter and skim milk powder as a milk protein (Patent references 4 and 5). However, the product described in Patent reference 4 is a fermented milk flavoring having a condensed-milk flavor and is not a taste improver having a flavor of fresh raw milk. Also, in the methods described in Patent references 4 and 5, skim milk powder is used as the milk protein. Since about 50% by mass or more of lactose is contained in skim milk powder, when heated for enzyme inactivation, sterilization and the like after the protease treatment, Maillard reaction which is a reaction of reducing sugars with amino acids is generated, thus posing a problem of causing generation of various odors such as a scorched odor, a caramel odor, and a nuts-like odor. In addition, the taste improver described in Patent Reference 5 is aimed at getting rid of a powdery odor by adding it at the time of producing bread and therefore is not a taste improver having a flavor of fresh raw milk.
A low antigenicity casein hydrolyzate having improved flavor and absorption property has been reported (Patent Reference 6). In addition, a taste improver for food or drink in which a protease treated product of milk serum protein was used in combination with a lipase-treated product of milk fat has also been reported (Patent Reference 7). However, those which are described in Patent References 6 and 7 are a taste improver and the like which mask a foul taste or a foul smell of food or drink. Thus, these were not the flavor enhancers which give a flavor of fresh raw milk (particularly a raw milk feeling) and a full body or a thickness of raw milk, totally in a good balance.    Patent Reference 1: JP-A-2004-267126    Patent Reference 2: JP-A-49-94875    Patent Reference 3: JP-A-62-151155    Patent Reference 4: Japanese Patent No. 2875825    Patent Reference 5: JP-A-5-49385    Patent Reference 6: Japanese Patent No. 3383461    Patent Reference 7: Japanese Patent No. 3274792